Short Message Service (SMS) is a text messaging service component of phone, web, or mobile communication systems, using standardized communications protocols that allow the exchange of short text messages between fixed line or mobile phone devices. SMS text messaging is the most widely used data application in the world, with 2.4 billion active users, or 74% of all mobile phone subscribers. The term SMS is used as a synonym for all types of short text messaging as well as the user activity itself in many parts of the world.

SMS as used on modern handsets was originated from radio telegraphy in radio memo pagers using standardized phone protocols and later defined as part of the Global System for Mobile Communications (GSM) series of standards in 1985 as a means of sending messages of up to 160 characters, to and from GSM mobile handsets. Since then, support for the service has expanded to include other mobile technologies such as ANSI CDMA networks and Digital AMPS, as well as satellite and landline networks. Most SMS messages are mobile-to-mobile text messages though the standard supports other types of broadcast messaging as well.

History

Initial concept

The idea of adding text messaging to the services of mobile users was not frequent in many communities of mobile communication services at the beginning of the 1980s. The first action plan of the CEPT Group GSM, approved in December 1982, requested "The services and facilities offered in the public switched telephone networks and public data networks... should be available in the mobile system". This target includes the exchange of text messages either directly between mobile stations, or transmitted via Message Handling Systems widely in use since the beginning of the 1980s.

The SMS concept was developed in the Franco-German GSM cooperation in 1984 by Friedhelm Hillebrand and Bernard Ghillebaert. The innovation in SMS is ''Short''. The GSM is optimized for telephony, since this was identified as its main application. The key idea for SMS was to use this telephony-optimized system, and to transport messages on the signaling paths needed to control the telephony traffic during time periods when no signaling traffic existed. In this way, unused resources in the system could be used to transport messages at minimal cost. However, it was necessary to limit the length of the messages to 128 bytes (later improved to 140 bytes, or 160 seven-bit characters) so that the messages could fit into the existing signaling formats.

This concept allowed SMS to be implemented in every mobile station by updating its software. This concept was instrumental for the implementation of SMS in every mobile station ever produced and in every network from early days. Hence, a large base of SMS capable terminals and networks existed when the users began to utilize the SMS. A new network element required was a specialized short message service center, and enhancements were required to the radio capacity and network transport infrastructure to accommodate growing SMS traffic.

Early development

The technical development of SMS was a multinational collaboration supporting the framework of standards bodies, and through these organizations the technology was made freely available to the whole world. This is described and supported by evidence in the following sections.

The first proposal which initiated the development of SMS was made by a contribution of Germany and France into the GSM group meeting in February 1985 in Oslo. This proposal was further elaborated in GSM subgroup WP1 Services (Chairman Martine Alvernhe, France Telecom) based on a contribution from Germany. There were also initial discussions in the subgroup WP3 network aspects chaired by Jan Audestad (Telenor). The result was approved by the main GSM group in a June '85 document which was distributed to industry. The input documents on SMS had been prepared by Friedhelm Hillebrand (Deutsche Telekom) with contributions from Bernard Ghillebaert (France Télécom).

SMS was considered in the main GSM group as a possible service for the new digital cellular system. In GSM document "''Services and Facilities to be provided in the GSM System''", Here a rudimentary description of the three services was given:

# Short message Mobile Terminated (SMS-MT)/ Point-to-Point: the ability of a network to transmit a Short Message to a mobile phone. The message can be sent by phone or by a software application. # Short message Mobile Originated (SMS-MO)/ Point-to-Point: the ability of a network to transmit a Short Message sent by a mobile phone. The message can be sent to a phone or to a software application. # Short message Cell Broadcast.

The material elaborated in GSM and its WP1 subgroup was handed over in Spring 1987 to a new GSM body called IDEG (the Implementation of Data and Telematic Services Experts Group), which had its kickoff in May 1987 under the chairmanship of Friedhelm Hillebrand (German Telecom). The technical standard known today was largely created by IDEG (later WP4) as the two recommendations GSM 03.40 (the two point-to-point services merged together) and GSM 03.41 (cell broadcast).

WP4 created a Drafting Group Message Handling (DGMH), which was responsible for the specification of SMS. Finn Trosby of Telenor chaired the draft group through its first 3 years, in which the design of SMS was established. DGMH had about five to eight participants, and Finn Trosby mentions as major contributors Kevin Holley, Eija Altonen, Didier Luizard and Alan Cox. The first action plan mentions for the first time the Technical Specification 03.40 “Technical Realisation of the Short Message Service”. Responsible editor was Finn Trosby. The first and very rudimentary draft of the technical specification was completed in November 1987. However, drafts useful for the manufacturers followed at a later stage in the period. A comprehensive description of the work in this period is given in.

The work on the draft specification continued in the following few years, where Kevin Holley of Cellnet (now Telefonica O2 UK) played a leading role. Besides the completion of the main specification GSM 03.40, the detailed protocol specifications on the system interfaces also needed to be completed.

Support in other architectures

The Mobile Application Part (MAP) of the SS7 protocol included support for the transport of Short Messages through the Core Network from its inception. MAP Phase 2 expanded support for SMS by introducing a separate operation code for Mobile Terminated Short Message transport. Since Phase 2, there have been no changes to the Short Message operation packages in MAP, although other operation packages have been enhanced to support CAMEL SMS control.

From 3GPP Releases 99 and 4 onwards, CAMEL Phase 3 introduced the ability for the Intelligent Network (IN) to control aspects of the Mobile Originated Short Message Service, while CAMEL Phase 4, as part of 3GPP Release 5 and onwards, provides the IN with the ability to control the Mobile Terminated service. CAMEL allows the gsmSCP to block the submission (MO) or delivery (MT) of Short Messages, route messages to destinations other than that specified by the user, and perform real-time billing for the use of the service. Prior to standardized CAMEL control of the Short Message Service, IN control relied on switch vendor specific extensions to the Intelligent Network Application Part (INAP) of SS7.

Early implementations

The first SMS message was sent over the Vodafone GSM network in the United Kingdom on 3 December 1992, from Neil Papworth of Sema Group (now Mavenir Systems) using a personal computer to Richard Jarvis of Vodafone using an Orbitel 901 handset. The text of the message was "Merry Christmas".

The first commercial deployment of a short message service center (SMSC) was by Aldiscon part of Logica (now part of Acision) with Telia (now TeliaSonera) in Sweden in 1993, followed by Fleet Call (now Nextel) in the US, Telenor in Norway and BT Cellnet (now O2 UK) later in 1993. All first installations of SMS gateways were for network notifications sent to mobile phones, usually to inform of voice mail messages. The first commercially sold SMS service was offered to consumers, as a person-to-person text messaging service by Radiolinja (now part of Elisa) in Finland in 1993. Most early GSM mobile phone handsets did not support the ability to send SMS text messages, and Nokia was the only handset manufacturer whose total GSM phone line in 1993 supported user-sending of SMS text messages.

Initial growth was slow, with customers in 1995 sending on average only 0.4 messages per GSM customer per month. One factor in the slow takeup of SMS was that operators were slow to set up charging systems, especially for prepaid subscribers, and eliminate billing fraud which was possible by changing SMSC settings on individual handsets to use the SMSCs of other operators.

Over time, this issue was eliminated by switch billing instead of billing at the SMSC and by new features within SMSCs to allow blocking of foreign mobile users sending messages through it. By the end of 2000, the average number of messages reached 35 per user per month, and by Christmas Day 2006, over 205 million messages were sent in the UK alone.

It is also alleged that the fact that roaming customers, in the early days, rarely received bills for their SMSs after holidays abroad had a boost on text messaging as an alternative to voice calls.

Text messaging outside GSM

SMS was originally designed as part of GSM, but is now available on a wide range of networks, including 3G networks. However, not all text messaging systems use SMS, and some notable alternative implementations of the concept include J-Phone's ''SkyMail'' and NTT Docomo's ''Short Mail'', both in Japan. Email messaging from phones, as popularized by NTT Docomo's i-mode and the RIM BlackBerry, also typically uses standard mail protocols such as SMTP over TCP/IP.

SMS today

In 2008, 4.1 trillion SMS text messages were sent. SMS has become a massive commercial industry, worth over $81 billion globally as of 2006. The global average price for an SMS message is 0.11 USD, while mobile networks charge each other interconnect fees of at least $0.04 when connecting between different phone networks.

Technical details

GSM

The ''Short Message Service – Point to Point (SMS-PP)'' was originally defined in GSM recommendation 03.40, which is now maintained in 3GPP as TS 23.040. GSM 03.41 (now 3GPP TS 23.041) defines the ''Short Message Service – Cell Broadcast (SMS-CB)'', which allows messages (advertising, public information, etc.) to be broadcast to all mobile users in a specified geographical area.

Messages are sent to a Short message service center (SMSC) which provides a "store and forward" mechanism. It attempts to send messages to the SMSC's recipients. If a recipient is not reachable, the SMSC queues the message for later retry. Some SMSCs also provide a "forward and forget" option where transmission is tried only once. Both mobile terminated (MT, for messages sent ''to'' a mobile handset) and mobile originating (MO, for those sent ''from'' the mobile handset) operations are supported. Message delivery is "best effort", so there are no guarantees that a message will actually be delivered to its recipient, but delay or complete loss of a message is uncommon, typically affecting less than 5% of messages. Some providers allow users to request delivery reports, either via the SMS settings of most modern phones, or by prefixing each message with *0# or *N#. However, the exact meaning of confirmations varies from reaching the network, to being queued for sending, to being sent, to receiving a confirmation of receipt from the target device, and users are often not informed of the specific type of success being reported.

Message size

Transmission of short messages between the SMSC and the handset is done whenever using the Mobile Application Part (MAP) of the SS7 protocol. Messages are sent with the MAP MO- and MT-ForwardSM operations, whose payload length is limited by the constraints of the signaling protocol to precisely 140 octets (140 octets = 140 * 8 bits = 1120 bits). Short messages can be encoded using a variety of alphabets: the default GSM 7-bit alphabet, the 8-bit data alphabet, and the 16-bit UTF-16 alphabet. Depending on which alphabet the subscriber has configured in the handset, this leads to the maximum individual short message sizes of 160 7-bit characters, 140 8-bit characters, or 70 16-bit characters (including spaces). GSM 7-bit alphabet support is mandatory for GSM handsets and network elements, but characters in languages such as Arabic, Chinese, Korean, Japanese or Cyrillic alphabet languages (e.g. Russian, Serbian, Bulgarian, etc.) must be encoded using the 16-bit UTF-16 character encoding (see Unicode). Routing data and other metadata is additional to the payload size.

Larger content (concatenated SMS, multipart or segmented SMS, or "long SMS") can be sent using multiple messages, in which case each message will start with a user data header (UDH) containing segmentation information. Since UDH is part of the payload, the number of available characters per segment is lower: 153 for 7-bit encoding, 134 for 8-bit encoding and 67 for 16-bit encoding. The receiving handset is then responsible for reassembling the message and presenting it to the user as one long message. While the standard theoretically permits up to 255 segments, 6 to 8 segment messages are the practical maximum, and long messages are often billed as equivalent to multiple SMS messages. See concatenated SMS for more information. Some providers have offered length-oriented pricing schemes for messages, however, the phenomenon is disappearing.

SMS Gateway providers

SMS gateway providers facilitate SMS traffic between businesses and mobile subscribers, including mission-critical messages, SMS for enterprises, content delivery, and entertainment services involving SMS, e.g. TV voting. Considering SMS messaging performance and cost, as well as the level of messaging services, SMS gateway providers can be classified as aggregators or SS7 providers.

The aggregator model is based on multiple agreements with mobile carriers to exchange two-way SMS traffic into and out of the operator's SMSC, also known as local termination model. Aggregators lack direct access into the SS7 protocol, which is the protocol where the SMS messages are exchanged. SMS messages are delivered to the operator's SMSC, but not the subscriber's handset; the SMSC takes care of further handling of the message through the SS7 network.

Another type of SMS gateway provider is based on SS7 connectivity to route SMS messages, also known as international termination model. The advantage of this model is the ability to route data directly through SS7, which gives the provider total control and visibility of the complete path during SMS routing. This means SMS messages can be sent directly to and from recipients without having to go through the SMSCs of other mobile operators. Therefore, it is possible to avoid delays and message losses, offering full delivery guarantees of messages and optimized routing. This model is particularly efficient when used in mission-critical messaging and SMS used in corporate communications.

Interconnectivity with other networks

Message Service Centers communicate with the Public Land Mobile Network (PLMN) or PSTN via Interworking and Gateway MSCs.

Subscriber-originated messages are transported from a handset to a Service Center, and may be destined for mobile users, subscribers on a fixed network, or Value-Added Service Providers (VASPs), also known as application-terminated. Subscriber-terminated messages are transported from the Service Center to the destination handset, and may originate from mobile users, from fixed network subscribers, or from other sources such as VASPs.

On some carriers non-subscribers can send messages to a subscriber's phone using an Email-to-SMS gateway. Additionally, many carriers, including AT&T, T-Mobile USA, Sprint, and Verizon Wireless, offer the ability to do this through their respective websites.

For example, an AT&T subscriber whose phone number was 555-555-5555 would receive e-mails from 5555555555@txt.att.net as text messages. AT&T subscribers can easily reply to these SMS messages, and the SMS reply is sent back to the original email address. Sending email to SMS is free for the sender, but the recipient is subject to the standard delivery charges. Only the first 1600 characters of an email message can be delivered to a phone, and only 160 characters can be sent from a phone.

Text-enabled fixed-line handsets are required to receive messages in text format. However, messages can be delivered to non-enabled phones using text-to-speech conversion.

Short messages can send binary content such as ringtones or logos, as well as Over-the-air programming (OTA) or configuration data. Such uses are a vendor-specific extension of the GSM specification and there are multiple competing standards, although Nokia's Smart Messaging is common. An alternative way for sending such binary content is EMS messaging, which is standardized and not dependent on vendors.

SMS is used for M2M (Machine to Machine) communication. For instance, there is an LED display machine controlled by SMS, and some vehicle tracking companies use SMS for their data transport or telemetry needs. SMS usage for these purposes is slowly being superseded by GPRS services due to their lower overall cost. GPRS is offered by smaller telco players as a route of sending SMS text to reduce the cost of SMS texting internationally.

AT commands

Many mobile and satellite transceiver units support the sending and receiving of SMS using an extended version of the Hayes command set, a specific command language originally developed for the Hayes Smartmodem 300-baud modem in 1977.

The connection between the terminal equipment and the transceiver can be realized with a serial cable (e.g. USB), a Bluetooth link, an infrared link, etc. Common AT commands include AT+CMGS (send message), AT+CMSS (send message from storage), AT+CMGL (list messages) and AT+CMGR (read message).

However, not all modern devices support receiving of messages if the message storage (for instance the device's internal memory) is not accessible using AT commands.

Premium-rated short messages

Short messages may be used to provide premium rate services to subscribers of a telephone network.

Mobile-terminated short messages can be used to deliver digital content such as news alerts, financial information, logos and ring tones. The first premium-rate media content delivered via the SMS system was the world's first paid downloadable ringing tones, as commercially launched by Saunalahti (later Jippii Group, now part of Elisa Group) in 1998. Initially only Nokia branded phones could handle them. By 2002 the ringtone business globally had exceeded one billion US dollars of service revenues, and nearly 5 billion dollars by 2008. Today, they are also used to pay smaller payments online, for example for file sharing services, in mobile application stores or VIP section entrance. Outside the online world, one can buy a bus ticket, bevarages from ATM, pay parking ticket, order a store catalog or some goods (e.g. discount movie DVDs) and many more.

Premium-rated messages are also used in Donors Message Service to collect money for charities and foundations. DMS was first launched at April 1, 2004 and is very popular in the Czech Republic, e.g. the Czech people sent over 1.5 million messages to help South Asia recover from 2004 Indian Ocean Earthquake.

The Value-added service provider (VASP) providing the content submits the message to the mobile operator's SMSC(s) using a TCP/IP protocol such as the short message peer-to-peer protocol (SMPP) or the External Machine Interface (EMI). The SMSC delivers the text using the normal Mobile Terminated delivery procedure. The subscribers are charged extra for receiving this premium content; the revenue is typically divided between the mobile network operator and the VASP either through revenue share or a fixed transport fee. Submission to the SMSC is usually handled by a third party.

Mobile-originated short messages may also be used in a premium-rated manner for services such as televoting. In this case, the VASP providing the service obtains a short code from the telephone network operator, and subscribers send texts to that number. The payouts to the carriers vary by carrier; percentages paid are greatest on the lowest-priced premium SMS services. Most information providers should expect to pay about 45% of the cost of the premium SMS up front to the carrier. The submission of the text to the SMSC is identical to a standard MO Short Message submission, but once the text is at the SMSC, the Service Center (SC) identifies the Short Code as a premium service. The SC will then direct the content of the text message to the VASP, typically using an IP protocol such as SMPP or EMI. Subscribers are charged a premium for the sending of such messages, with the revenue typically shared between the network operator and the VASP. Short codes only work within one country, they are not international.

An alternative to inbound SMS is based on long numbers (international number format, e.g. +44 762 480 5000), which can be used in place of short codes for SMS reception in several applications, such as TV voting, product promotions and campaigns. Long numbers work internationally, allow businesses to use their own numbers, rather than short codes which are usually shared across a lot of brands. Additionally, long numbers are non-premium inbound numbers.

SMS in satellite phone networks

All commercial satellite phone networks except ACeS and OptusSat support SMS. While early Iridium handsets only support incoming SMS, later models can also send messages. The price per message varies for different networks. Unlike some mobile phone networks, there is no extra charge for sending international SMS or to send one to a different satellite phone network. SMS can sometimes be sent from areas where the signal is too poor to make a voice call.

Satellite phone networks usually have web-based or email-based SMS portals where one can send free SMS to phones on that particular network. Other commercial service providers such as Targlets allow for SMS on the +881 and +882 numbering plan prefix. Some other providers also cover the +870 plan.

Unreliability

Unlike dedicated texting systems like the Simple Network Paging Protocol and Motorola's ReFLEX protocol , SMS message delivery is not guaranteed, and many implementations provide no mechanism through which a sender can determine whether a SMS message has been delivered in a timely manner . SMS messages are generally treated as lower-priority traffic than voice, and various studies have shown that around 1% to 5% of messages are lost entirely, even during normal operation conditions, and others may not be delivered until long after their relevance has passed . The use of SMS as an emergency notification service in particular has been starkly criticized .

Vulnerabilities

The Global Service for Mobile communications (GSM), with the greatest worldwide number of users, succumbs to several security vulnerabilities. In the GSM, only the airway traffic between the Mobile Station (MS) and the Base Transceiver Station (BTS) is optionally encrypted with a weak and broken stream cipher (A5/1 or A5/2). The authentication is unilateral and also vulnerable. There are also many other security vulnerabilities and shortcomings. Such vulnerabilities are inherent to SMS as one of the superior and well-tried services with a global availability in the GSM networks. SMS messaging has some extra security vulnerabilities due to its store-and-forward feature, and the problem of fake SMS that can be conducted via the Internet. When a user is roaming, SMS content passes through different networks, perhaps including the Internet, and is exposed to various vulnerabilities and attacks. Another concern arises when an adversary gets access to a phone and reads the previous unprotected messages.

In October 2005, researchers from Pennsylvania State University published an analysis of vulnerabilities in SMS-capable cellular networks. The researchers speculated that attackers might exploit the open functionality of these networks to disrupt them or cause them to fail, possibly on a nationwide scale.

SMS spoofing

The GSM industry has identified a number of potential fraud attacks on mobile operators that can be delivered via abuse of SMS messaging services. The most serious of threats is SMS Spoofing. SMS Spoofing occurs when a fraudster manipulates address information in order to impersonate a user that has roamed onto a foreign network and is submitting messages to the home network. Frequently, these messages are addressed to destinations outside the home network – with the home SMSC essentially being “hijacked” to send messages into other networks.

The only sure way of detecting and blocking spoofed messages is to screen incoming mobile-originated messages to verify that the sender is a valid subscriber and that the message is coming from a valid and correct location. This can be implemented by adding an intelligent routing function to the network that can query originating subscriber details from the HLR before the message is submitted for delivery. This kind of intelligent routing function is beyond the capabilities of legacy messaging infrastructure.

Emergency Services

In some countries SMS messages can be used to contact the emergency services. In the United Kingdom, SMS text messages can be used to contact the local emergency services provider after registering with the emergency SMS service. This service is primarily aimed at people who by reason of disability are unable to make a voice call but has recently been promoted as a means for walkers and climbers to call emergency services from areas where a voice call is not possible due to low signal strength. Such service is also available in Hong Kong.

See also

Comparison of mobile phone standards

SMS language

Telegram

Text messaging

Thumbing

Short Message Service Center (SMSC)

Short message service technical realisation (GSM)

SMS gateways (sending text to or from devices other than phones)

SMS hubbing

SMS home routing

Multimedia Messaging Service

Extended Messaging Service

References

External links

3GPP – The organization that maintains the SMS specification.

SMS, the strange duckling of GSM

ISO Standards (In Zip file format)

GSM 03.38 to Unicode – the official GSM

SMS FAQs (GSM-Technology.com) – includes definitions of Class 0, Class 1, Class 2 and Class 3 MT (Mobile Terminated) messages

SMS PDU mode (PDU = Protocol Description Unit)

Category:3rd Generation Partnership Project standards Category:Mobile telecommunication services Category:Mobile telecommunications standards Category:Text messaging

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